<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
    
  </style>
</head>
<body>
  
</body>
<script>
  
  console.log(NaN === NaN)

  console.log( isNaN( NaN ) )

  console.log( isNaN( 365 ) )

  console.log( isNaN( "hello" ) )
  
  console.log( isNaN( "365" ) )
  
  console.log( isNaN( "36a5" ) )

</script>
</html>